Static and Dynamic Models of Formation Water in Sincor Area, Orinoco Belt, Venezuela

摘要

Sincor is a strategic association between PDVSA, Total and Statoil, committed to the production, upgrading and commercialization of extra heavy oil from an area covering over 325 Km2 in the Orinoco Belt (Figure 1). The Sincor area is composed of a series of stacked unconsolidated sand-shale reservoirs with good petrophysical properties. The depositional system can be divided in two main parts, Deltaic and Fluvial. Fluvial sands, mainly stacked braided channels, represent the bottom part of the reservoir. Deltaic sands go from distributary channel and mouth bar to point bar and crevasse splay. Drilling of vertical observation wells and a testing campaign started at the end of 1999. In well tests, anomalies in water salinity values were observed: an aquifer salinity of 2300 ppm, while some wells produced water at 15000 ppm. At that time, high values were considered measurement problems. In 2001, the first horizontal producers started to cut water with similar high values to those observed in some well tests. Since then a multidisciplinary study was launched aiming at defining and characterizing all water sources using well tests (15 vertical wells) and water production data (150 horizontal wells). This information has then been integrated with geological interpretation and reservoir characterization. In this paper a static model is developed using well test information from the area. The model explains why different ranges of water salinities were observed in the oil and water zones. This model was corroborated qualitatively with log information. Dynamic data confirmed and detailed further the initial model. An exponential decrease of water salinity is generally observed with increasing water production or water cut. This phenomenon is explained by probable water influx in the form of fingering from the low salinity aquifer continously displacing high salinity formation water. The exponential curve shape would depend on the tortuosity and length of the path between the water and the produced oil zones. Static and dynamic data are consistent and confirm our model of water production mechanism observed in the field.